Radiation therapy has been employed to treat tumorous tissue. In radiation therapy, a high energy beam is applied from an external source towards the patient. The external source, which may be rotating (as in the case for arc therapy), produces a collimated beam of radiation that is directed into the patient to the target site. The dose and placement of the dose must be accurately controlled to ensure that the tumor receives sufficient radiation, and that damage to the surrounding healthy tissue is minimized.
Sometimes during a radiation therapy, the patient may be undergoing breathing motion. In such cases, it may be desirable to compensate for breathing motion during the treatment delivery session such that radiation may be properly delivered, or ceased to be delivered, to the target region. For example, if the patient's breathing becomes non-periodic (e.g., due to sudden movement such as coughing), then it may be desirable to stop a delivery of radiation. Compensating for breathing motion has two components: 1) determining the location of radiotherapy target, and 2) controlling component(s) of a radiation system, e.g., by turning the therapy beam on-off as in gating, redirecting the beam as in multi-leaf collimator (MLC) tracking, moving the patient support as in couch tracking, or a combination of the above.
There is a latency associated with current techniques of localizing the target. This is because current localization methods have a latency resulting from data acquisition and another latency resulting from the processing delays. There is also latency in the controlling of the components of a radiation system, such as mechanical motion required to either redirect the treatment beam or to reposition the patient. Applicant determines that in order to make the compensation for breathing motion temporally and geometrically accurate the overall latency from both the target localization and the controlling of machine components need to be overcome. In order to compensate for breathing motion, Applicant determines that it would be desirable to provide new techniques for predicting breathing signal, so that the overall latency from target localization and controlling of machine components can be overcome.
Also, unconstrained and normal breathing motion of a lung target is only approximately periodic and subject to variation in time. These changes can be a combination of baseline drift and breath-to-breath changes in amplitude and period in the order of 10 percent or more. More sudden changes caused by coughing or swallowing will result in even larger deviations from the normal breathing pattern. Sometimes, audio or visual coaching techniques can reduce these variations, but a 10 percent change is normal even after implementing these techniques in the clinic. Applicant of the subject application determines that there is a need to quantify the degree of non periodicity of breathing resulting from above variations, since it is expected to affect the performance of any prediction algorithm, and therefore the accuracy of determining the target position for management of motion. Also Applicant determines that it would be desirable to have a fast responding and prospective measure of non periodicity that can be used to interrupt the treatment beam when a sudden deviation from normal breathing pattern occurs. In order to compensate for deviation from periodicity (e.g., due to coughing), Applicant determines that it would be desirable to provide new techniques for determining non-periodicity.
Also, in current radiation therapy techniques, the internal target region is periodically imaged (e.g., using x-ray) to verify the position of the internal target region during a treatment session. Applicant determines that periodically imaging of internal target region is not desirable because it increases radiation dose delivered to the patient. Thus, Applicant also determines that it would be desirable to provide a technique for triggering imaging process that is non-periodic.